Desired open-circuit voltage increase enables efficiencies approaching 19% in symmetric-asymmetric molecule ternary organic photovoltaics

The large open-circuit voltage (V_oc) loss is currently the main obstacle for pursuing the highly efficient organic photovoltaics (OPVs). To address this issue, we construct the ternary OPVs (TOPVs) consisting of symmetric BTP-eC9 and asymmetric BTP-S9 acceptors with similar absorption profiles and demonstrate it as a feasible way to increase V_oc via reducing the energetic disorder and non-radiative decay. This strategy enables a desired higher voltage in TOPVs than those in both binary OPVs, without sacrificing absorbing range. Besides, the ternary blend exhibits enhanced charge transport property due to stronger π-π stacking than binary films, resulting in the enhanced fill factor (FF). Consequently, the optimal TOPV exhibits a champion efficiency of 18.8% (certified as 18.7%) with a high voltage of 0.861 V and a high FF of 79.34%, representing the best among certified single-junction OPVs. This work demonstrates an effective approach to increase V_oc, paving the way toward high-efficiency OPVs.